If you’re installing a forward facing car seat, you may notice a gap behind the lower back of the seat. That gap is usually fine and just due to the shape of the car seat, but here are 4 things to check to be sure:
-Recline setting
-Seat bottom flat on the vehicle seat
-Overhang limit
-Inch Test your install at the belt path

If all of those things are good to go, that gap is not a problem!